Technical Field
The present disclosure relates to a pen-shaped position pointer (stylus) and a signal processor for detecting a condition of the position pointer on a sensor that capacitively couples with the position pointer.
Description of the Related Art
A pen-shaped position detector is used, for example, to enter text and drawings. In this case, there is a demand to not only enter coordinate values as an input but also enter angular information such as rotation and tilt of the position pointer based, for example, on the manner in which the user twists his or her hand or on the personal habit as data.
To respond to this demand, disclosures have been proposed, for example, in Patent Document 1 (Japanese Patent Laid-Open No. 2014-35631) and Patent Document 2 (U.S. Pat. No. 8,638,320B2 specification) which are designed to detect the tilt angle of the position pointer on the sensor surface of the position detector or the rotation angle of the position pointer about the axis vertical to the sensor surface.
In Patent Document 1, first and second electrodes are provided on a core body to detect the rotation angle of the position pointer. The first and second electrodes are alternately selected to change the electrode from which to transmit an AC (alternating current) signal. At this time, signal transmission pattern information is included in the AC signal transmitted from the position pointer. The signal transmission pattern information indicates from which of the first and second electrodes the AC signal is transmitted. Then, the position detector calculates the rotation angle of the position pointer about the axis vertical to the sensor surface on the basis of a plurality of coordinate positions on the sensor surface on which the AC signal from the position pointer has been received. The coordinate positions are found in relation to pattern information received from the position pointer.
Further, in Patent Document 1, three electrodes are provided on a housing to detect the tilt angle of the position pointer so that the tip portion on one side of the housing surrounds the core body that protrudes from an opening of the housing. Moreover, a switching circuit is provided which supplies an AC signal to one of the electrodes selected on the basis of a predetermined pattern. Then, the position pointer transmits, to the position detector, pattern information indicating the pattern type when the pattern is changed by the switching circuit. Then, the position detector calculates the tilt angle of the position pointer relative to the sensor surface from at least three coordinate positions and three signal strengths that are obtained for at least three pieces of pattern information received.
Still further, in Patent Document 2, a signal is supplied to tip electrodes (414 and 714) and surrounding electrodes (ring electrode 416 and segment electrodes 716-A to 716-C) to detect the rotation and tilt angles of the position pointer (stylus) on the basis of signal reception patterns from the tip electrodes on the touch panel and signal reception patterns from the surrounding electrodes.
As described in the above Patent Documents 1 and 2, there is a demand for a capacitive coupling position pointer which is designed to point a position on the sensor by capacitively coupling with the sensor of the position detector to be able to detect a rotation condition (rotation angle) of the position pointer itself on the sensor surface and the tilt angle of the position pointer relative to the sensor surface. Then, recent years have seen a demand for this type of capacitive coupling position pointer to go beyond basic capabilities such as detecting the position pointed to when the tip of the core body (electrode) comes in contact with the sensor surface and to be able to detect the position pointed to by the position pointer when the tip of the core body (electrode) of the position pointer is in so-called hovering condition in which the tip of the core body is away from the sensor surface.
In the position pointer described in Patent Document 1, however, when the tip of the core body is away from the sensor surface of the position detector, that is, in a so-called hovering condition, the first and second electrodes provided on the core body are not used. Signals are transmitted to the sensor from the three electrodes provided to surround the core body. As a result, signals are not necessarily transmitted from the position pointer to the sensor in an efficient manner. Therefore, it is difficult for the position detector to detect the position pointer that is away from and is hovering over the sensor surface with high sensitivity.
In the case of the position pointer described in Patent Document 2, signals are transmitted not only from the surrounding electrodes but also from the tip electrodes, thus allowing for highly efficient transmission of signals from the position detector to the sensor. In the position pointer described in Patent Document 2, however, a signal is always transmitted to the sensor from the tip electrodes and all of the surrounding electrodes irrespective of whether the position pointer is in contact with or hovers over the sensor surface, thus resulting in large power consumption. This type of position pointer is battery-driven. Therefore, the power consumption problem is important.